The present invention relates to a motor for carrying out PWM sensorless driving and to a disk drive apparatus using the motor.
FIG. 21 is a block diagram showing the configuration of a conventional motor. The operation of the conventional motor will be described briefly by using this FIG. 21. A rotor 1010 has a field part formed of a permanent magnet and generates a rotation force by virtue of interaction with three-phase windings 1011, 1012 and 1013. A power supplying part 1020 comprises three high-side power transistors and three low-side power transistors. The respective high-side and low-side power transistors are connected in series, and one terminal of each winding of a phase is connected to the connection point. The power supplying part 1020 comprising the high-side power transistors and the low-side power transistors supplies electric power to the windings 1011, 1012 and 1013. A position detecting part 1030 compares the terminal voltages V1, V2 and V3, each generated at one terminal of each of the windings 1011, 1012 and 1013, with the common voltage Vc generated at the other terminals, and outputs a position detection pulse signal FG in response to the result of the comparison. A commanding part 1040 outputs a speed command signal EC for controlling the speed of the rotor 1010 to a switching controlling part 1050. The switching controlling part 1050 outputs a PWM signal Wp for high-frequency switching the power transistors of the power supplying part 1020 to an activation controlling part 1060 in response to the speed command signal EC of the commanding part 1040. The activation controlling part 1060 outputs activation control signals N1, N2, N3, M1, M2 and M3 for controlling activation to the windings 1011, 1012 and 1013 to the power supplying part 1020 in response to the position detection pulse signal FG of the position detecting part 1030 and the PWM signal Wp of the switching controlling part 1050. Hence, the power supplying part 1020 supplies activation-controlled electric power to the windings 1011, 1012 and 1013, whereby the rotor 1010 is driven by PWM sensorless operation.
In addition, in the conventional motor, in order that the detection of the rotor position is prevented from malfunctioning, an output signal subjected to masking depending on high-frequency switching operation is used as a position detection signal for activation switching. A conventional motor having this kind of configuration is disclosed in the gazette of Japanese unexamined Patent Application, Publication No. Hei 11-4595, for example.
In the conventional motor configured as described above, when high-frequency switching operation is OFF, the neutral point of the windings is pulled to the power supply voltage or the ground voltage, whereby it is difficult to carry out position detection operation. As a motor for solving this kind of problem, a motor having a different configuration, such as the motor disclosed in the gazette of Japanese unexamined Patent Application, Publication No. Hei 0.8-223970, is available. In this conventional motor, position detection operation was carried out only during the ON operation of high-frequency switching operation.
However, the configuration of the above-mentioned conventional motor has problems described below. In the conventional motor, the position detecting part 1030 compares the terminal voltages V1, V2 and V3, each generated at one terminal of each of the windings 1011, 1012 and 1013, with the common voltage Vc, and outputs the position detection pulse signal FG to the activation controlling part 1060 in response to the result of the comparison; the activation controlling part 1060 outputs high-side activation control signals N1, N2 and N3 and low-side activation control signals M1, M2 and M3 to the power supplying part 1020 in response to the position detection pulse signal FG. Hence, the power supplying part 1020 supplies electric power to the windings 1011, 1012 and 1013, thereby carrying out the sensorless driving of the motor. Therefore, when the position detecting part 1030 erroneously detects the position of the rotor at the beginning of starting, sensorless driving is carried out while activation control is done according to the information detected erroneously; hence, there was a problem of having a high possibility of causing a starting failure in the conventional motor.
Since the position of the rotor is indefinite and the rotation speed thereof is low at the beginning of starting, the counter electromotive voltages induced in the windings 1011, 1012 and 1013 are small, and it is difficult to accurately detect the position of the rotor. Hence, in the sensorless driving of the conventional motor, a starting failure may occur, resulting in a serious problem. In particular, in the case when the motor is started by PWM sensorless operation, since an induced voltage owing to the change in current due to PWM operation is superimposed on the terminal voltage of a detection phase, the position of the rotor is erroneously detected under the influence of the induced voltage generated at the time of PWM sensorless starting, whereby a starting failure may occur. Hence, as another conventional motor, an apparatus is available that is configured so as to be started after the rotor is attracted to a specific phase at the time of starting so that its position is fixed. In the motor having this kind of configuration, rotor movement time for initial position fixing is required; this causes a problem of extending starting time.